Composite hierarchical anti-disturbance control for dynamic positioning system of ships based on robust wave filter

The composite hierarchical anti-disturbance control (CHADC) strategy is investigated for dynamical position system of ships(DP) with multiple disturbances, which include slowly varying environmental disturbances, first-order wave-induced disturbances and additional disturbances. The ship's velocities and the slowly varying environmental disturbances are estimated by designing state observer and disturbance observer, respectively. Subsequently, a robust wave filter (RWF) is constructed to deal with the first-order wave-induced disturbances, which assures a prescribed performance level for the filter error system. The CHADC strategy is proposed by integrating stochastic disturbance observer-based control (DOBC) theory, RWF method with H & INFIN; control, such that high control accuracy of the DP system can be realized. Efficacy of the proposed control strategy is illustrated through the example of a supply ship.